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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.unix.questions,comp.lang.c
Subject: Re: Fork and Join, Pipe in C
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Date: Sun, 21-Jun-87 17:57:13 EDT
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Posted: Sun Jun 21 17:57:13 1987
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(Again, we redirect this to comp.unix.questions/INFO-UNIX.)

> If vfork is much faster (as opposed to slightly faster) than fork, it is
> time to complain to the supplier of your Unix, asking why he hasn't
> implemented fork efficiently.  Even Berkeley *intended* to fix this, as
> witness the comments on the vfork manual page.  Sensible vendors have
> long since implemented copy-on-write fork, which eliminates most of the
> copying involved in fork, thus eliminating most of the reason to use the
> ugly and brain-damaged vfork.

Or, at least, sensible vendors that are implementing on hardware that
provides the ability to specify, with a relatively small granularity,
regions of a process' address space such that attempts to modify them
will cause traps.  If, for example, you are stuck with
write-protecting the entire data or stack segment, copy-on-write may
not buy you much.  Fortunately, most machines don't impose obnoxious
restrictions of that flavor.

The only remaining reason to use vfork is that one has written ugly
and brain-damaged code that depends on the semantics of "vfork".
Such code does, unfortunately, exist; one of the pre-releases of
4.3BSD used this crock in "find", but it was fixed before 4.3BSD went
out the door in its final form.  If anybody has written code of this
sort, they should hang their head in shame and then go out and fix it
NOW.
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com